Smith, 38, was charged Friday in Snohomish County Superior Court with first-degree murder in the slaying of Susann Smith, 37.

Deputy prosecutor Craig Matheson wrote that Alan Smith carefully planned the attack and made “extensive efforts” to research and then clean up forensic evidence.

Susann Smith was found dead in her home on Feb. 12.

Autopsy reports indicate Susann Smith could have been beaten with a rubber mallet. The weapon hasn’t been found. An ex-girlfriend of Alan Smith’s reportedly told police he had a similar mallet when they were dating. Searches of his home and vehicles didn’t find a mallet.

Bothell detectives obtained roughly 15 search warrants as they built their case.

Bloody footprints and shoeprints found at the scene reportedly matched Alan Smith’s feet and shoes he had recently purchased, court papers said.

Smith was arrested in June. A local minister told police that the pair were friends. They were discussing the killing, and Smith told him, “Yes, I did it to her.”

The conversation did not take place under any kind of confidential religious circumstances, the minister said.

The minister came forward after Smith didn’t go to police as he anticipated.

Susann Smith was sleeping in the home’s master bedroom when she was attacked, Matheson said in court papers filed earlier this year. She was beaten and stabbed and then dragged into the bathroom.

Her body then was placed in the bathtub. The killer filled the bath and held her under water. Water was found in her lungs.

An autopsy also documented more than 22 individual head injuries, including a fatal skull fracture.

Alan Smith is being held on $1 million bail. Matheson on Friday asked a judge to require that if Smith posts bail, he must post at least $100,000 in cash.

Smith has no criminal history. He’s expected to be arraigned Monday.

He also has a pending Bothell Municipal Court case regarding his alleged obstruction of the murder investigation when he refused a judge’s order to turn over his passport. The passport later was seized.